Advanced passive and active methods for vibration control in rotating machines

Effective control of vibration in rotating machinery is a major concern in many industries and research institutions. With the ever-increasing drive for higher operating speeds, the need for developing vibration mitigation methods that cater for the arduous operating conditions that consequently arise is paramount. Phenomena that may have been insignificant in relatively low-speed rotating machines begin to gain importance with increasing speed, an example of which is the gyroscopic effect. This thesis is aimed at enriching the knowledge base on rotordynamic vibration control. Independent Modal Control (IMC) is addressed, within the context of rotating machinery. A study is performed on various actuation technologies that may be used to implement active vibration control. The well-known problem of balancing rotating machinery is also considered. The first-order modal filters based on Structure Preserving Transformations (SPTs) are capable of decoupling a rotor dynamic system into individual modes of vibration, such that IMC may be performed. Unlike traditional control schemes, the method based on first-order modal filters does not require the imposition of highly restrictive conditions on the system (classical damping). As a result, gyroscopic effects - which are substantial in high-speed rotating machinery - and non-classical damping may be fully accounted for in the modal domain. The main problem pertaining to this method arises from the fact that the response of the controlled system is linked with the stability of the modal filters. As such, if the filters are unstable, the controlled response is eventually overcome by noise. This thesis explores the spectral properties of the modal filter with a view to understanding the factors that affect its stability; some interesting findings on the filter eigenvalues are presented. Furthermore, the question as to whether filter stability is an essential requirement is addressed. The relationship between the rotordynamic system and the modal filter is also investigated. An illustration of the techniques developed in relation to IMC using first-order modal filters is presented in the form of a FE simulation on a realistic aero-engine model. The implementation of active vibration control in a dynamic system is realised through the application of control forces by actuators. In the case of rotating machines, these would normally be located at the bearings. Actuation may be achieved from a variety of technologies such as electromagnetic, piezoelectric, magnetostrictive, ultrasonic etc. This thesis conducts a study on some popular actuation technologies, with the aim of finding an effective alternative to the ubiquitous squeeze film damper. The merits and drawbacks of the various technologies are compared. Also, some novel design concepts are proposed, and (in some cases) their viability demonstrated through calculations. It is well-known that rotor unbalance is usually the main source of vibration in rotating machines. Thus, improvements in procedures for balancing such machines are continuously being sought. With increasing in-service operating speeds and ever more stringent standards, traditional balancing methods progressively become inadequate. One of the reasons for this is the inability of balancing tests to capture the contribution of patterns of unbalance that excite higher modes of vibration, as the tests speeds are usually lower than in-service speeds. This thesis proposes a robust balancing approach that utilises additional information on rotor unbalance, in the form of a covariance matrix, to improve the balancing procedure. The method is illustrated in a FE model of a rotating machine, and is shown to be superior to the traditional method.EThOS - Electronic Theses Online ServiceGBUnited Kingdo